This invention relates to a system for detecting the speed of an engine for a vehicle.
A vehicle includes an engine, a clutch, a transmission (gear box) and wheels. The clutch, the transmission and the wheels are connected to the engine in this order. The amount of supply of fuel to the engine is controlled by an actuator such as a stepping motor.
A controller comprising a microcomputer and so on is mounted on the vehicle. The controller serves to control the actuator for controlling the fuel supply amount. In the case where the vehicle is provided with an automatic transmission, the controller also serves to control actuators for driving the automatic transmission, the clutch, etc.
When the controller is to control, for example, the stepping motor so as to control the amount of supply of fuel to the engine, the actual engine speed is an indispensable information. Therefore, a rotation sensor is associated with an output shaft of the engine or a shaft always connected with the engine. The rotation sensor outputs pulses in accordance with the operation of the engine. The above controller calculates the actual engine speed in accordance with the above pulses.
However, when the rotation sensor is subjected to malfunction, the engine speed information is not obtained, and as a result the fuel supply control and other controls can not be carried out properly.
Japanese Laid-Open (Kokai) Patent Application No. 232354/86 discloses a controller provided with two rotation sensors for outputting pulses in accordance with the operation of the engine. One of the two rotation sensors is used as a main sensor for detecting the engine speed whereas the other is used as a back-up sensor. In this case, if the main sensor operates properly, the back-up sensor does not perform any practical function, and therefore is useless or impractical.
Japanese Laid-Open Patent Application No. 67243/87 discloses a rotation sensor connected to an input shaft or an output shaft of a transmission. Japanese Laid-Open Patent Application No. 57845/88 discloses an arrangement in which the relation between the rotational position of a stepping motor and the engine speed is constant when the engine is idling (that is, under no load). Japanese Laid-Open Patent Application No. 162959/85 discloses two rotation sensors for detecting the engine rotation. By checking the relationship of output signals of these two rotation sensors, malfunction of each sensor is detected.